Apparatus for railway train communication systems



March 22, 1938. A. J. SORENSEN 2,111,647

APPARATUS FOR RAILWAY TRAIN COMMUNICATION SYSTEMS Filed Oc t. 22, 1936 2 Sheets-Sheet 2 F PB 5 15w 8 r I Motion Actuazeol Device Converzen Oscillator.

Mas tar M5 wilch l 1 Power Oscillaton 0S INVENTOR Andrew orensen.

HIS ATTORNEY Patented Mar. 22, 1938 UNETED STATES PATENT OFFICE APPARATUS FOR RAILWAY TRAIN COM- IVIUNICATIGN SYSTEMS Application ()ctober 22, 1936, Serial No. 106,969

12 Claims.

My invention relates to apparatus for railway train communication systems, and particularly to apparatus for combined code signaling and telephone systems for railway trains.

I will describe one form of apparatus embodying my invention, and will then point out the novel features thereof in claims.

In railway train communication systems of the type here contemplated, a carrier frequency current modulated with voice frequencies is used for telephone communication. For code signaling, a carrier modulated by a single predetermined voice frequency or its equivalent is used. In either case, the same carrier frequency is used for transmission in both directions. The communication channel preferably includes the track rails in the manner described and claimed in the United States application for Letters Patent, Serial No. 450,135, filed May 1, 1930 by L. O. Grondahl for Electric train signaling systems. Communication current is supplied to and received from the communication channel through the medium of circuit elements electrically coupled with the track rails. Switching apparatus .is provided at each station for selectively coupling either the transmitting apparatus or the receiving apparatus to the track rails. In systems heretofore proposed, the operator manually actuates such switching apparatus, especially during telephone communication, and there is no limit imposed on the length of time the equipment of a station can be left in the position for transmitting a telephone current. Hence, the operator at one station is unable to break in to either speak or signal to an operator at the other station when he is transmitting a telephone conversation. It is desirable that either operator may interrupt the conversation of the other operator in order that a message may be delivered relating to the control of the train without delay. For example, where the train brakes are to be governed at two different locations on a train through the medium of the communication system, it is desirable that the operator at either station may order a change in the'brake condition without delay,

Accordingly, a feature of my invention is the provision of novel and improved apparatus for systems of the type here under consideration wherewith an operator at the station-receiving a telephone message may breakin upon the conversation of the operator talking. Another feature of my invention is the provision of novel and improved apparatus for systems of the type here involved by means of which'apparatus a number of different channel frequencies can be provided so that each train of a railroad can have a distinctive channel frequency of its own and interference between different trains is avoided. Other features and advantages of my invention will appear as the specification progresses.

In the accompanying drawings, Figs. 1 and 2, when taken together, constitute a diagrammatic view of one form of apparatus embodying my invention when applied to a railway train for telephone and code signaling, the code signaling being utilized for governing the operation of the train brakes. The apparatus of Fig. 1 is that to be installed on the train at the location of the supervising operator, which location may be, for example, the locomotive of a freight train, the engineman being the supervising operator. The apparatus of Fig. 2 is that installed at another location on the train, which location may be the caboose of a freight train, the train brakes being manually controlled at the caboose by a trainman in accordance with code signals received from the locomotive.

In the following description, like reference characters refer to similar parts in each of the two views.

In certain instances, circuit. controlling con tact fingers are shown remote from the relay windings or other devices which operate them. The relationship between these elements is indicated by the fact that each such circuit contact finger bears a reference character corresponding to the reference character of the associated relay or device plus a distinctive numeral, and each such contact finger is illustrated in the position corresponding to the position of the relay or device.

Referring to Fig. l, the reference character EV designates the usual engineers brake valve capable of establishing the release, running, lap, service and emergency conditions of the brake pipe pressure. As shown schematically, a circuit contact assembly is associated with the brake valve EV, the contact members [2 and I23 of which assembly are connected to and actuated by handle I3 of the brake valve. The contact member [2 is adapted to engage an arcuate contact M in all positions of handle I3, to engage an arcuate contact H3 in release, running and lap positions of the brake valve; and to engage an arcuate contact l6 in the service and emergency positions. The contact member I23 is adapted to engage the arcuate contacts l2l and I22 in the release, running and lap positions.

The reference character MS designates a threeposition circuit controlling master switch. The

three positions of the switch are indicated by the numerals i, 2, and 3. The numerals l, 2, and 3 are placed on the drawings only in connection with the contact 32 of the switch for the sake of clearness, and it will be understood that the other contacts 35, 35, 3?, 38, 39, and 53 of the switch MS are each adaptable of movement to three corresponding positions. The position No. l of the switch MS, that is, the position illustrated in Fig. 1, is the normal position of the switch to which it returns under the action of a biasing spring not shown when not manually held at either its No. 2 or No. 3 position. When the switch MS is in the No. 1 position the locomotive equipment is capable of being actuated either automatically or manually between the transmitting and receiving conditions to send and receive code signaling impulses in a manner to appear hereinafter. The No. 2 position of the switch is selected when it is desired to send a telephone current, and the No. 3 position of the switch sets the equipment in a condition for receiving a telephone current.

The locomotive equipment includes a mechanically tuned oscillator or coder N. The type of coder is immaterial and it may be that disclosed in the United States Letters Patent No. 1,858,876, granted May 17, 1932 to P. N. Bossart for Coding apparatus. It will sufiice for this description to say that the operating winding 4 of the coder N is continuously supplied with current from a battery 5 over its own contact member 6, with the result that the contact members I and 8 of the coder are continuously oscillated between a left-hand position illustrated by solid lines and a right-hand position illustrated by dotted lines at a predetermined rate, say, for example, 120 times per minute. The contact member I engages a contact 9 when swung to its left-hand position and the contact member 8 engages a contact ill when swung to its right-hand position. As will shortly appear, time is divided into sending and receiving periods by the contact members 'i and 8 under the normal position of the master switch MS and with the brake valve EV set at the release, running or lap position. Under the No. 2 and No. 3 positions of the master switch MS, and also when the brake valve is operated to the service and emergency posi tions, the coder N is ineifective.

Two independent inductor coils CC and V are mounted on the locomotive in inductive relation with the track rails. These coils are preferably of the air core type and may be mounted on the top of the locomotive tender. It follows that communication current flowing in the track rails induces electroniotive forces in the inductor coils CC and V0. As will later appear, the coil CC is utilized for reception of code signaling current and the coil V0 is utilized for reception of telephone current.

Both code signaling and telephone currents are supplied to the track rails through the medium of a sending circuit directly coupled with the rails, and which circuit may be traced from the secondary winding ll of an output transformer T over wire l1, rear tender truck wheels !8, track rails l9, forward truck wheels 20, and wire 2| to the opposite terminal of the secondary winding It is clear that in response to an electromotive force induced in the secondary winding II, in a manner to be described, current is supplied to the track rails with the result that such current is transmitted along the track rails in both drections from the locomotive in the wellknown manner.

A manually operated dial selector switch DS by which different channel frequencies for code signaling are obtained for different trains is provided. In this instance, this selector switch DS comprises five contact members, 23, 24, 25, 26, and 2'! which are operatively connected together as indicated by a dotted line, the several contact members being insulated from each other in any convenient manner. The selector switch DS has four distinctive positions to which the five contact members may be set by rotation in a clockwise direction, as viewed in Fig. 1, the contacts being illustrated as set at the first one of the four positions. Each of the five dial contact members controls four condensers so that any one of the four associated condensers may be included in a circuit with which the contact member is associated. For example, the contact member 23 in the first position of switch DS, that is, in the position illustrated, connects a condenser 40 between the wires 4i and 42 of an associated circuit, and rotation of the contact member 23 in the clockwise direction includes condensers 43, B4, and 45 in the same circuit for the second, third and fourth positions of the selector switch, respectively. In a similar manner, rotation of the contact members 24, 25, 26, and 2'! to the diiferent positions connects different condensers in the associated circuits, as will be understood by an inspection of Fig. 1. The manner wherewith the different positions of the selector switch DS are effective to adjust the associated equipment for different channel frequencies will appear as the system is described.

The transmitting apparatus on the locomotive includes a code frequency generator or oscillator OSI, a power amplifier PA, a voice converter CO, and a microphone M.

The oscillator OSI is preferably an electron tube oscillator of the well-known Hartley type. The oscillating circuit comprises a reactor 22 and any one of the four condensers 40, 43, 44 or 45 in accordance with the position of the selector switch DS, as well as condenser I09, which condenser |09 is interposed in the circuit over a back contact H0 of a relay Ill to be referred to later. That the invention may be better understood, I shall assume by Way of illustration that the reactor 22 and the condensers 40, 43, 44, and 45, as well as the condenser I09, are so proportioned that the carrier frequencies generated by the oscillator OSI are I000, 6000, 5000, and 4000 cycles per second for the first, second, third and fourth positions of the selector switch DS, respectively, these respective carrier frequencies serving as channel frequencies for the four respective positions of the switch DS.

Furthermore, I shall asume that when relay H I is operated to open back contact H0 and remove condenser l09 from the oscillating circuit of oscillator OSI, the channel frequency supplied by the oscillator OSI is varied a few cycles, say, 50 cycles. By way of illustration, when the selector switch DS is set at its first position and the channel frequency is 7000 cycles, operation of relay III to remove condenser I09 from the oscillating circuit raises the channel frequency to 7050 cycles. Consequently, periodic operation of relay I l l to periodically disconnect the condenser I09 causes the channel frequency to be varied or Wobbled.

The power amplifier PA may be any one of several types, for example, it may be two power electrontub'es connected in the usual push-pull arrangement. The power amplifier PA is shown conventionally for the sake of simplicity since its specific structure forms no part of my present invention. When the master switch MS is set at its No. 1 position and the brake valve EV is operated, to either the release, running or lap position, the input terminals of the power amplifier PA are connected with the code oscillator 7 OS! over the code contact member I; and the output terminals of the power amplifier are connected with the primary winding 28 of the output transformer Tl through a filter selectively tuned to efiiciently pass the channel frequency. Under these conditions, theinput circuit for the power amplifier PA may be traced from the right-hand terminal of the oscillating circuit of oscillator OS! over wires 29 and 52, code contact L0, wire 30, contacts I5, I2, and M of the contact assembly, wire 3|, contact 32 of the master switch MS in its No. 1 position, wire 33, input side of the power amplifier PA, and wire 3 to the left-hand terminal of the oscillating circuit. The output circuit of the power amplifier PA extends from its lower right-hand terminal over wire 46, primary winding 28 0f transformer Tl, contact 35 of the master switch, wire M, contact member 24 of the selector switch DS in its first position, condenser 48, reactor 49, and to the lower left-hand terminal of the power amplifier. The condenser 48 and reactor 49 are so proportioned that the above traced output circuit is tuned to efiiciently pass-the generated frequencies of the oscillator OSI, which, as here assumed, are 7000 cycles with selector switch DS at the first position. and relay lll released, and 7050 when relay iii is operated. It follows that as long as the brake valve EV is set at a running position and the master switch MS is at its No. 1 position and relay Ill is released, an impulse of current of 7000 cycles is supplied to the primary winding 28 of transformer Ti during each period the code contact 1-9 is closed. Each such impulse of code signaling current supplied to the primary winding 28 of transformer Ti induces electromotive forces in the secondary windings H and 50 of that transformer, the secondary winding ll being interposed in the sending circuit for supplying current to the rails as pointed out hereinbefore. The secondary winding 50 is connected with the input terminals of a rectifier 5!, the output terminals of which are connected with an operating winding of a relay VR, with the result that the relay VB. is energized during each outgoing impulse. The function of the relay VR will be referred to hereinafter.

With the brake valve EV operated to either its service or emergency position when the switch MS is in its No. 1 position, the connection extending from wire 52 and. including contacts l6, I2 and M of the contact assembly provides a shunt path around the code contact 1-9, with the result that code signaling current from the code oscillator CS1 is continuously supplied to the track rails and to the relay VR.

The relay III is controlled over its own back contact H3 and a contact H4 of a common spring return push button PB. Depressing push button PB causes relay Ill to be operated and contact H0 is periodically opened and closed to periodically disconnect the condenser E00 from its associated oscillating circuit. Depressing push button PB also closes contact H5 and com pletes, when the master switch MS is in its No. 1 position, the input circuit of the power amplifier PA, irrespective of the operation of the coder and position of the brake valve. As set' forth previously, removal of the condenser Hi9 from the oscillating circuit causes the carrier frequency supplied by the oscillator OS! to be varied 50 cycles. Thus, operation of the push button, when the selector switch DS is set at its first position and the master switch is in its No. 1 position, is effective to supply to the track rails code signaling current having a frequency varied between 7000 and Z050 cycles.

When the master switch MS is operated to its No. 2 position the input of the power amplifier PA is shifted to include the voice converter CO and its output is shifted to exclude the filter l849. The output circuit now consists of lower right-hand terminal of amplifier PA, wire 46, primary winding 28, contact 35 of master switch MS in'its No. 2 position, back contact ERS of a relay RS to be referred to later, and thence to the lower left-hand terminal of the amplifier. The input circuit maynow be traced from the lower right-hand terminal of the voice converter (30 over wire 54, contact 32 of the switch MS in its No. 2 position, back contact iRS, wire 33, input side of power amplifier PA, and wires 34 and 42 to the lower left-hand terminal of the voice converter. The input terminals of the voice converter C0 are connected with the microphone M over a simple circuit easily traced. The voice converter CO may be any one of several types, such as, for example, a balanced electron tube modulator wherewith a carrier frequency generated therein is modulated by the voice frequencies and the carrier and one side band are suppressed, leaving the remaining side band to be supplied to its output circuit. The voice converter CO is shown conventionally only since its specific structure forms no part of my present invention.

To fix the ideas, I shall assume the carrier frequency generated within the voice converter CO is 7000 cycles per second, the voice frequencies utilized extend from 500 to 2500 cycles, and that the upper side band is transmitted. In this case, the transmitted carrier telephone current has the frequency range of 7500 to 9500 cycles. It follows that by shifting the master switch MS to its N0. 2 position and speaking into the microphone causes a side band carrier telephone current of the frequency range of 7500 to 9500 to be supplied to the track rails, a portion of the outgoing energy being rectified and utilized for energizing the relay VR.

It is well known that even apparently sustained speech contains short intervals when the energy of the speech is only a small fraction of the average volume. This being so, the relay VB. is deenergized or is energized at so low a value that it is released during each pause in the conversation. The relay VB is proportioned and adjusted for relatively quick acting characteristics. For example, a pause of the order of 0.1 second frequently occurs in a conversation and relay VB is adjusted to release at something less than 0.1 second. The pickup period of the relay would be of the order of 0.02 second. Hence, during the sending of a telephone current the relay VB is picked up during speaking periods, is released during normal pauses that occur at the end of a phrase, and is again picked up on the first syllable of the next group of words. The relay VB is also released, of course, during sustained pauses in the conversation. The function of such operation of the relay VR will appear hereinafter.

The receiving apparatus of Fig. 1, which includes a loud. speaker LS, an amplifier demodulator DM, an oscillator CS2 and several filters, will now be described.

. The amplifier demodulator DM may be any one of several types, among them being a balanced electron tube demodulator with one or more stages of amplification, and it is shown conventionally only for the sake: of simplicity. With the master switch MS in its No. 1 position and the brake valve EV set at a running position, the inductor coil CC is interposed in an input circuit network of the demodulator DM over the code contact 8-H]. Starting from the inductor coil CC a circuit may be traced over wire 55, code contact 8-!0, contacts l2l-l23l22, Wire 50, condenser 51, contact member 25 of switch DS, lower portion of reactor 58, condenser 59, contact member 28 of switch DS, upper portion of reactor 60, wire 6|, a normally closed contact PBI of the push button PB, and back to the coil CC. The input terminals of demodulator DM are connected across the reactor 60 over a circuit including wire 62, contact 3'! of switch MS, wire 63, reactor 60, and wire 54. The reactors 58 and 60, together with the condensers 57 and 59, constitute a filter for tuning the input circuit network to pass the channel frequency of the code signaling current. With the selector switch DS set at its first position as illustrated in Fig. 1, this filter would be proportioned to pass a code signaling current of 7000 to 7050 cycles, which are the same as the frequencies delivered by the oscillator OSI, it being recalled that the same channel frequency is used for transmission in both directions.

When the master switch MS is shifted to its No. 2 position to bring contacts 36 and 3'! to their respective No. 2 positions, this input circuit network for the demodulator DM is completed at the front contact 3R8 of relay RS and a back contact IVR of relay VR. Consequently, the locomotive equipment is also conditioned to receive code signaling current during pauses in the transmission of a telephone current from the locomotive, since the relay VB is released during each pause as explained hereinbefore and relay RS is picked up during each pause in a manner shortly to appear.

The oscillator 082 is preferably similar to the oscillator OS! and the carrier current generated thereby is applied to the demodulator DM for demodulation purposes. The frequency delivered by the oscillator CS2 is governed by the position of the selector switch DS and the position of the master switch MS and relay RS. A condenser is permanently connected across a reactor 61 to form an oscillating circuit for oscillator OS2, and one of four additional condensers is interposed in this oscillating circuit in accordance with the position of contact 21 of the selector switch DS to adjust the oscillator CS2 to the channel frequency. With switch DS set at its first position, a condenser 68 is connected in parallel with condenser 65, the connection for condenser 68 being completed either by contact 39 of switch MS in its No. 1 position or by the front contact 4R8 of relay BS. The current generated by oscillator CS2 is delivered to the demodulator DM through the medium of a winding 66 coupled with reactor 61 of the oscillating circuit. The parts are so proportioned that the carrier frequency generated by the oscillator 082 during code signaling is of a frequency which is different from the channel frequency, say, 1000 aiiresv cycles less. Thus, when the selector switch DS is set at its first position to select a channel frequency of 7000 cycles, the frequency generated by oscillator 082, when the master switch is set at its No. 1 position or when the front contact 4R8 is closed, is 6000 cycles per second. On the assumption that the second, third and fourth positions of the selector switch DS are effective to select channel frequencies of 6000, 5000, and 4000 cycles per second, respectively, the current generated by the oscillator CS2 is of 5000, 4000, and 3000 cycles per second for the second, third and fourth positions of the selector switch, respectively. The condenser 65 is so proportioned that when it alone is interposed in the oscillating circuit the carrier frequency generated by the oscillator CS2 is the same as the carrier frequency of the telephone current and in this instance is of 7000 cycles per second. Consequently, when the selector switch is set at its first position and the master switch MS is set either at its No. 1 position or at its No. 2 position, and the relay RS is picked up, that is, the positions in which the input circuit for the demodulator DM is conditioned to receive the code signaling current of 7000 cycles, the oscillator 0S2 supplies to the demodulator a current of 6000 cycles, with the result that the output of the demodulator is a current of 1000 cycles. When the code signaling current is varied between 7000 and 7050 cycles in the manner explained hereinbefore, the output of the demodulator is a current which varies between 1000 and. 1050 cycles. When the input circuit for the demodulator DM is conditioned, in a manner shortly to appear, to receive a carrier telephone current of the range of 7500 to 9500 cycles, the oscillator 0S2 delivers a current of 7000 cycles to the demodulator and the voice frequencies appear in the output of the demodulator.

The loud speaker LS is normally connected with the output terminals of the demodulator DM through a filter 59, which filter is proportioned to pass a current of 1000 to 1050 cycles. It is clear, therefore, that a note is sounded at the loud speaker during such periods as a code signaling current is picked up from the track rails, the note being of a steady pitch when the frequency of the code signaling current is uniform and being varied in pitch when the frequency of the code signaling current is varied.

In the No. 3 position of the master switch M8 the inductor coil V0 in connected to the input terminals of the demodulator DM through a band pass filter BPF having a pass band of 7500 to 9500 cycles, the connection between the filter BPF and the demodulator DM being completed by the contact 3'! of the switch MS in the No. 3 position. With the master switch MS moved to its No. 3 position, the contact 38 thereof completes a connection by which the loud speaker LS is connected directly with the output terminals of the demodulator. As set forth hereinbefore, operation of the switch MS away from its No. 1 position to open contact 39 increases the carrier current generated by oscillator CS2 to the frequency of 7000 cycles. Consequently, an upper side band telephone current of 7500 to 9500 cycles picked up by the coil VC is demodulated and the resultant audio frequencies are reproduced by the loud speaker LS.

With the master switch MS in its No. 2 position, the contact 30 completes a circuit by which a reactor 10 and a. condenser H are connected with the output terminals of the demodui it) lator DM in parallel with the loud speaker. The reactor 70 and condenser 7| are proportioned to pass frequencies of the order of 10'00 to 1050 cycles. A portion of the reactor 70 is connected with the input terminals of a rectifier T2, the output terminals of which are connected with the winding of a relay 13'. Hence, when the master switch MS is at its No. 2 position and a current of 1000 to 1050 cycles appears in the output of the demodulator DM, the relay i3 is energized, as well as a note being sounded by the loud speaker. p

i For controlling the relay RS, the contacts 5R5, ZRS, 3RS and GRS of which are utilized at times for switching the locomotive equipment as pointed out hereinbefore, a motion responsive means is provided. This motion responsive means com; prisesa motion actuated device 77 and relays l5 and 75. The motion actuated device Tl may take different forms and is effectively operated in response to motion of the locomotive due to the vibration created by the locomotive in motion, or due to a connection with a moving part of the locomotive As here shown, the motion actuated device i7 is a microphone of the type disclosed in my United States Letters Patent No. 1,834,077, granted December 3, 1931, and which microphone is mounted in any convenient manner so as to be vibrated in response to an appreciable speed of the locomotive. The essential parts of the microphone I? are two metal electrodes E and El spaced apart in an insulation housing 78, the space between the electrodes being partly filled 'at least with carbon granules. When the micro phone TI is not vibrated the resistance between the electrodes E and El through the: carbon granules is relatively low, but when the microphone is vibrated the resistance between the electrodes is increased many times its normal value. The relay 75 is provided with a circuit extending from the B terminal of any convenient source of current such as a battery not shown, over winding of relay l5, electrodes and carbon granules of microphone Ti and to the C terminal of the same source of current. The parts are so proportioned that relay 75 is energized and picked up when the microphone Tl is not vibrated but when the microphone H is vibrated in response to motion of the locomotive, the energization of the relay is so reduced that the relay is released to close its back contact 19.

The relay RS is provided with a control circuit extending from the B battery terminal over back contact E9 of relay l5, winding of relay RS, back contact 80 of relay 76, back contact 8! of relay VR, contact 53 of switch MS in its No. 2 position, and thence to the C battery terminal. This control circuit for relay RS may also be completed over the front contact 14 of relay 73, as will be readily understood by an inspection of Fig. 1. Relay 16 is controlled over a circuit including back contact 18 of relay 15, winding of relay 76, front contact 82 of relay RS, back contact 8i of relay VR and contact 53 of switch MS.

During transmission of a telephone current with the locomotive in motion, the switch MS is set at its No. 2 position and the relay VB is picked up, with the result that the relays RS and 6 are deenergized since the relay E3 is now also released. During a pause in the telephone conversation the relay VB. is deenergized and releases to close its back contact 8!. Under this condition the relays RS and 16 are picked up in turn. With relay 70 picked up the relay R8 is deenergized and releases. to open the circuit for relay but the relay it remains picked up for a period since it is slow releasing in character. This cycle of operation of relays RS and I0 is repeated as long as the pause in the transmission of telephone conversation continues. Relays RS and 76 are proportioned to allow relay RS to remain energized for a suitable length of time, for ekample, 0.1 second, and to allow a suitable period between successive operations of rela} "6, for example, 1 second.

During the "period the relay RS is picked up the receiving apparatus on the locomotive is conditioned for the reception of the code signaling current as describedhereinbefore. In the event code signaling current appears at the locomotive and is picked up by the inductor coil CC, the relay 73 is energized and the loud speaker sounds a corresponding note. With relay l3 picked up the relay RS is retained energized to retain the apparatus in the receiving condition as long 'as the code signaling current continues to be received. Furthermore, further transmission of telephone current is prevented since the transmitting apparatus is disconnected at the back contacts IRS and 2R8. If no 'code sigii'aling current appears, relay RS drops, followed by relay 76 at the end of its release period and the transmission of the telephone current is renewed. To prevent loss of essential parts in the speech, the relays RS and it are proportioned so as'to repeat their cycle of operation at least once every second, as explained above.

Referring to Fig. 2, the caboose is provided with equipment similar to the equipment on the locomotive except that the coder is replaced by three relays, 83, 84, and 85; and the brake valve EV is not interlocked with the circuits. The relays 83, 84, and 85 are effective to synchronize the caboose equipment with the 1000- motive equipment during the normal operation of the system. That is, the caboose equipment is, through the action of the relays 83, 84, and 85, alternately shifted between its transmitting and receiving positions instep with the locomotive equipment, the caboose equipment being conditioned for receiving during the sending periods of the locomotive equipment and being condi-, tioned for transmitting during the receiving periods of the locomotive equipment. It is believed unnecessary to describe the apparatus of Fig. 2 in detail since it would be a repetition of that of Fig, 1, and it is thought that the caboose apparatus can best be understood by a description of the operation of the system.

In describing the operation of the system, I shall first consider the normalv condition, that is, the condition where both master switches MS are set at their respective No. 1 positions, the selector switches DS being both set at the first position as illustrated in the drawings so that the channel frequency selected is, as here assumed, 7000 cycles per second. Furthermore, I shall assume that the brake valves EV are both positioned at the running position for the train and that the train is in motion so that the relay 75 of each motion actuated means. is released. When the coder N is operated to its left-hand position as illustrated, the closing of code contact l-9 completes the input circuit between the oscillator OSl and the power amplifier PA and an impulse of code signaling current is supplied to the track rails. Relay VR on the locomotive is also energized and picked up byv a portion of the outgoing energy, but operation of relay VR.

at this time performs no useful function and need not be further considered. When this code signaling impulse appears at the caboose an electromotive force is induced in its inductor coil CC and is applied to the input of the caboose amplifier demodulator DM, the input circuit for the demodulator DM being first completed at back contact 86 of relay and then at front contact 81 of relay 83 after the relays 83, 84, and 85 have been operated. At the start of the impulse the relays 83, 84, and 85 are all down and the input circuit network includes coil CC, back contact 86, wire 88; filter consisting of condenser 89, contact member 90, lower portion of reactor 9|, condenser 92, contact member 93 and upper portion of reactor 94; and thence back to the coil CC over wire Ill. The input terminals of the demodulator DM are connected across the reactor 94 over contact 95 of the master switch MS in its No. 1 position. Since the caboose oscillator CS2 is now supplying a current of 6000 cycles per second to the demodulator DM for mixing with the incoming code signaling impulse of 7000 cycles per second, a current of 1000 cycles is supplied to the loud speaker and a corresponding note is sounded. A circuit including a reactor 96 and a condenser 91 is also connected across the output terminals of the caboose demodulator DM in parallel with the loud speaker, this circuit being completed by the contact 98 of the master switch MS in its No. 1 position. The reactor 96 and condenser 9'! are proportioned to pass current of 1000 to 1050 cycles and hence current is supplied to the winding of relay 83 through rectifier 99 and that relay is energized by a portion of the output of the demodulator DM resulting from the code signaling impulse picked up from the track rails. Relay 83 on picking up causes the two relays 84 and 85 to be energized and picked up in turn, the circuit for relay 84 being completed at front contact I00 of relay 83 and the circuit for relay 85 being completed at the front contact I8I of relay 84. Relays 83, 84, and 85 now all remain energized as long as the code impulse continues, since the input circuit network is held closed at front contact 8! of relay 83.

When the coder N swings to its right-hand position the sending of the code signaling impulse is discontinued and the locomotive equipment is switched to its receiving condition. The caboose relay 83 is deenergized and immediately releases at the expiration of the code signaling impulse. Relay 84 releases shortly after relay 83 but relay 85 does not release until the expiration of its slow release period, this latter relay being slow releasing in character. During the period that relay 84 is down and relay 85 is up, the caboose oscillator OSI is connected with the input of the power amplifier PA over front contact I02 of relay 85 and back contact I03 of relay 84, the contact I84 of the master switch in its No. 1 position being also interposed in the circuit. Since the output circuit of the power amplifier PA on the caboose is now completed through primary winding I05 of the caboose transformer TI by contact I06 of the master switch, an electromotive force is induced in each of the secondary windings I01 and I 08 of the output transformer TI, and a corresponding impulse of code signaling current is supplied to the track rails and to the winding of the caboose relay VR. Operation of the caboose relay VR at this time accomplishes no useful function and need not be further considered. The code signaling impulse supplied to the track rails at the caboose is effective to induce an electromotive force in the locomotive inductor CC, which inductor is now connected with the input circuit network of the locomotive amplifier demodulator DM over the contact 8-) of the coder, with the result that a note is sounded at the loud speaker. The parts are so proportioned and adjusted that the relay 85 is released and the impulse sent from the caboose is discontinued, and the caboose apparatus is switched back to its receiving condition prior to the time the coder N operates back to its left-hand position. Consequently, impulses of the code signaling current are alternately exchanged automatically between the locomotive and the caboose as long as the normal condition of the equipments is maintained. This exchange of impulses indicates to the trainman in the caboose that a running position of his brake valve EV is to be effected. Such exchange of code impulses also indicates that the system is in proper operating condition.

Movement of the locomotive brake valve EV to either the service or emergency position causes the locomotive equipment to continuously send the code signaling current with the result that the caboose equipment is continuously held at the receiving condition and a corresponding note is sounded without interruption at the loud speaker. An uninterrupted audible signal of this pitch is an indication to the trainman in the caboose that the brake applying position of his brake valve EV is required.

The selector switches DS being both set at their first position, the several devices of the equipment of the locomotive and of the caboose are adjusted to operate on a channel frequency of 7000 cycles. In the event these two selector switches are each set to the second position the condensers interposed in the several associated circuits are such that the equipment at the two ends of the train are operated on a different channel frequency such as, for example, 6000 cycles per second. The third position of the switches adjusts the equipment to the channel frequency of, say, 5000 cycles; and the fourth position of the switches adjusts the equipment to the channel frequency of, say, 4000 cycles per second. Hence, four different trains, all similarly equipped, may each be provided with a distinctive channel frequency for its code signal system by the proper setting of the selector switches,

any caboose equipment being operative with any one of the different locomotive equipments. If more than four different channel frequencies are desired, the selector switches can be readily provided with additional positions and condensers provided for these additional positions that will adjust the equipment to still different channel frequencies.

I shall next consider the case where the engineman desires to telephone to the trainman in the caboose. The procedure would preferably be as follows. The engineman first shifts his master switch MS to the No. 3 position and places his equipment in speech receiving condition. This operation on the locomotive causes the sending of the normal code impulses to cease. On the caboose no note will be sounded at the loud speaker, the absence of which will indicate to the trainman that telephone communication with him is desired. The trainman will first shift his master switch to its No. 2 position, which places the caboose equipment in the speech sending condition. The trainman now verbally informs the engineman that he is ready to telephone by speaking the usual hello signal. After sending such signal the trainman immediately shifts his master switch to its No. 3 position. The engineman, upon receipt of such signal from the trainman, will shift his master switch to its N0. 2 position and initiate the conversation. From this point on telephone communication between the two ends of the train will be accomplished by the operators actuating their master switches be tween the No. 2 and No. 3 positions. At the termination of the telephone conversation the master switches at both locations will be released and returned to their No. 1 positions and code signaling will be reestablished. If the trainman in the caboose desires to initiate telephone communication, the procedure would be similar to that described above and need not be repeated.

If, during an interval the trainman is talking, the engineman desiresto break in on his conversation and verbally deliver an order to the trainman, the procedure is as follows, it being recalled that it has been assumed that the train is in motion. The engineman restores his master switch to its No. 1 position and depresses the push button PB. Operation of the push but 5 ton PB causes the locomotive equipment to continuously supply to the track rails the code sig naling current, but with wobbled frequency. On the first pause in the trainmans conversation the caboose relay VB is released and the relay RS is picked up over back contact l is of the associated relay 16, back contact I20 of relay VR and contact I24 of switch MS. Thus, the caboose equipment is, during the pause, momen tarily switched to its code receiving condition by virtue of the front contacts IRS, BRS, and 9R8 of relay RS since the caboose master switch MS is now set at its No. 2 position. This code signaling current of wobbled frequency induces an electromotive force in the caboose coil CC, and is applied to the demodulator DM since the relays 83, 84, and 85 are now all deenergized. The output of the caboose demodulator is now a current of 1000 cycles periodically varied a few cycles with the result that the note sounded by the loud speaker is varied in pitch. Furthermore, the relay 83 is picked up by a .portion of the output of the demodulator and the caboose relay RS is retained energized over the front contact H 3 of relay 83 so that the caboose apparatus is held at'its receiving condition as long; as this current continues to appear in the track rails. The trainman, upon receiving an audible signal, varied in pitch, would shift his master switch to its No. 3 position ready to receive any message i from the engineman. The engineman, after having depressed his push button PB for a reasonable interval, would release the push button and operate his master switch to its No. 2 position and convey the message he desires to send.

In the event, during an interval when the trainman is talking, an emergency should arise on the locomotive that required an application of the train brakes the engineman would operate his brake valve to a brake applying position and at the same time release the master switch MS.

Code signaling current of the channel frequency is now continuously supplied to the track rails, which current is picked up at the caboose on the first pause in the trainmans conversation in the manner explained above, and a corresponding note is sounded at the loud speaker and the relay 83 is retained energized. This note continues as long as the brake valve on the locomotive is retained at a brake applying position. An audible signal, steady in pitch, informs the trainman that an application of the train brakes is required and he would operate his brake Valve accordingly.

In the event the trainman in the caboose desires to break in upon the engineman during their telephone conversation, he would release his master switch MS and depress the push button PB to close contact H3 and operate relay HI, the operation of which relay causes the caboose equipment to supply to the rails code signaling current periodically varied in frequency from the channel frequency, the connection of oscillater 08! to the amplifier PA being completed at contact 525 of push button PB. During the first pause in the enginemans conversation the locomotive relay VB, is released and the associated relay RS is picked up, with the result that the locomotive receiving apparatus is made effective through the medium of the front contacts 3R8 and @RS of relay RS and back contact WE of relay VB, since switch MS is now at its No. 2 position. The electromotive force induced in the locomotive coil'CC in response to this code signaling current supplied to the rails at the caboose is now applied to the locomotive demodulator and demodulated and a note varied in pitch is sounded by the loud speaker. A portion of the received energy is supplied to the relay l3 and the relay 73 is picked up to complete at its front contact M the circuit for the relay RS. Such an audible signal received on a locomotive informs the engineman that the caboose trainman'desires to break in upon the conversation to deliver a message and the engineman would shift his master switch to its No. 3 position to receive whatever message the trainman may wish to send.

In the event the train is standing still and telephone communication is effected, the motion actuated devices render the relays RS inefiective.

Although in the foregoing description I have assumed definite channel frequencies and also definite carrier frequencies for the telephone current, it will be understood that my invention is not limited to these specific frequencies and they may be selected as desired.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In communication systems for railway trains the combination comprising, a train-can ried equipment mounted on a vehicle of a train including transmitting apparatus capable of supplying a periodic communication current and receiving apparatus responsive to such communication current as well as manually operable means effective to render either the transmitting apparatus or the receiving apparatus active, motion responsive means mounted on the train and effectively operated when the train is in motion, and circuit means controlled by said motion re sponsive means to place at times the receiving apparatus in an active condition irrespective of said manually operated means.

2. In communication systems for railway trains the combination comprising, a train-carried equipment mounted on a vehicle of a train including transmitting apparatus capable of supplying a periodic communication current and receiving apparatus responsive to such communication current as well as manually operable means effective to render either the transmitting apparatus or the receiving apparatus active, motion responsive means mounted on the train and effectively operated when the train is in motion, and circuit means controlled in part by said motion responsive means to place the receiving means in an active condition for an interval when said manually operated means is set to render the transmitting apparatus active.

3. In communication systems for railway trains the combination comprising, a train-carried equipment mounted on a vehicle of a train including transmitting apparatus capable of supplying a periodic communication current and receiving apparatus responsive to such communica tion current as well as manually operable means effective to render either the transmitting apparatus or the receiving apparatus active, a relay, circuit means to connect a winding of the relay with the transmitting apparatus to energize the relay with a portion of the outgoing communication current, motion responsive means mounted on the train and eiiectively operated when the train is in motion, and means controlled jointly by said relay and said motion responsive means to place the receiving apparatus in an active condition for an interval.

4. In communication systems for railway trains the combination comprising, a train-carried equipment mounted on a vehicle of a train including transmitting apparatus capable of supplying a periodic communication current and receiving apparatus responsive to such communication current as well as manually operable means effective to render either the transmitting apparatus or the receiving apparatus active, a relay, circuit means to connect a winding of the relay with the transmitting apparatus to energize the relay with a portion of the outgoing communication current, motion responsive means mounted on the train and effectively operated when the train is in motion, and means controlled jointly by said relay and said motion responsive means to periodically place the receiving apparatus in an active condition during an interruption in the outgoing communication current.

5. In communication systems for railway trains the combination comprising, a train-carried equipment mounted on a vehicle of a train including transmitting apparatus capable of supplying a periodic communication current and receiving apparatus responsive to such communication current as well as manually operable means effective to render either the transmitting apparatus or the receiving apparatus active, a relay, circuit means to connect a winding of the relay with the transmitting apparatus to energize the relay with a portion of the outgoing communication current, motion responsive means mounted on the train and effectively operated when the train is in motion, means controlled jointly by said relay and said motion responsive means to periodically place the receiving apparatus in an active condition during an interruption in the outgoing communication current, and means controlled by the receiving apparatus to retain itself in the active condition when cmrent is received during an interruption of the outgoing communication current.

6. In communication systems for railway trains the combination comprising, a train-carried equipment mounted on a vehicle of a train including transmitting apparatus capable of supplying a periodic communication current and receiving apparatus responsive to such communication current as well as manually operable means effective to render either the transmitting apparatus or the receiving apparatus active, a relay, circuit means to connect a winding of the relay with the transmitting apparatus to energize the relay with a portion of the outgoing communication current, motion responsive means mounted on the train and effectively operated when the train is in motion, means controlled jointly by said relay and said motion responsive means to periodically place the receiving apparatus in an active condition during an interruption in the outgoing communication current, and means controlled by the receiving apparatus to retain itself in the active condition and to establish a signal when current is received during an interruption of the outgoing communication currentv 7. In communication systems for railway trains the combination comprising, a train-carried equipment mounted on a vehicle of a train including transmitting apparatus capable of supplying a code signaling current or a telephone current and receiving apparatus responsive to such code signaling and telephone currents as well as manually operable means effective to place the equipment in condition to send the telephone current, a relay, circuit means to connect a winding of the relay with the transmitting apparatus to energize the relay with a portion of the outgoing telephone current, motion responsive means mounted on the train and effectively operated when the train is in motion, and means controlled jointly by said relay and said motion responsive means to place the receiving apparatus in a condition to receive code signaling current during a pause in the telephone conversation.

8. In communication systems for railway trains the combination comprising, a train-carried equipment mounted on a vehicle of a train including transmitting apparatus capable of supplying a code signaling current or a telephone current and receiving apparatus responsive to such code signaling and telephone currents as well as manually operable means efiective to place the equipment in condition to send the telephone current, means mounted on the train and including an element which increases its electrical resistance when vibrated in response to the train in motion, a relay having a control circuit including said element to deenergize the relay when the train is in motion, and means controlled in part by said relay to at times place the receiving apparatus in the condition to receive code signaling current when the manually operated means is set to place the equipment in a condition to transmit telephone current.

9. In communication systems for railway trains the combination comprising, a train-carried equipment mounted on a vehicle of a train including transmitting apparatus capable of supplying a code signaling current or a telephone current and receiving apparatus responsive to such code signaling and telephone currents as well as manually operable means effective to place the equipment in condition to send the telephone current, means mounted on the train and including an element which increases its electrical resistance when vibrated in response to the train in motion, a relay having a control circuit including said element to deenergize the relay when the train is in motion, another relay, circuit means to connect a winding of said other relay with the transmitting apparatus to energize the relay during a telephone conversation but which relay is deenergized during normal pauses in the telephone conversation, and means controlled jointly by said two relays when both relays are deenergized to render the receiving apparatus efiective to receive code signaling current.

10. In communication systems for railway trains utilizing the same carrier frequency for transmission in both directions the combination comprising, two train-carried equipments one at each of two spaced locations on a train and each equipment including transmitting apparatus and receiving apparatus, each transmitting apparatus including an oscillator to generate current of said carrier frequency and a power amplifier having a filter adjusted topass said carrier frequency interposed in its output circuit, each receiving apparatus including a demodulator having a filter adjusted to pass the carrier frequency interposed in its input circuit and a signaling device responsive to a given audio frequency interposed in its output circuit as well as an oscillator to generate a carrier frequency which differs from the transmitted carrier frequency by said audio frequency for mixing with the transmitted carrier, means partly at each location to cause said equipments to exchange impulses of current for signaling between the two locations; and a selector switch at each location having a first circuit member associated with the transmitting oscillator, a second circuit member associated with the power amplifier filter, a third and a fourth circuit member associated with the demodulator filter'and a fifth circuit member associated with the receiving oscillator, and said switches each capable of being set at any one of several different positions to rent of said carrier frequency and a power amplifler having a filter adjusted to pass said carrier frequency interposed in its output circuit,

each receiving apparatus including a demodulator having a filter adjusted to pass the carrier frequency interposed in its input circuit and a signaling device responsive to a given audio frequency interposed in its output circuit as well as an oscillator to generate a carrier frequency which difiers from the transmitted carrier frequency by said audio frequency for mixing with the transmitted carrier, means partly at each location to cause said equipments to exchange impulses of current for signaling between the two locations; a first set of condensers at each location associated with the transmitting oscillator, a second set of condensers at each location associated with the power amplifier filter, a third set of condensers at each location associated with the demodulator filter, a fourth set of condensers at each location associated with the receiving oscillator; and a selector switch at each location to selectively control the first, second, third and fourth sets of condensers toselect any one of everal different carrier frequencies for the communication system of the train.

12. In communication systems for railway trains the combination comprising, two traincarried equipments one at each of two spaced locations on a train, each equipment including transmitting apparatus and receiving apparatus, each transmitting apparatus capable of supply ing a code signaling current of a first or a second frequency as well as a telephone current, each receiving apparatus selectively responsive to code signaling current of said first and second fre quencies as well as to the telephone current to produce a first or a second signal as well as the telephonemessage, a relay at each of said locations, circuit means for each relay to connect a winding of the relay with the associated transmitting apparatus to energize the relay with a portion of the outgoing telephone current, means controlled by each relay to place at times the associated receiving apparatus in a condition to receive code signaling'current, and manually operable means at each location and each efiective to cause the associated transmitting apparatus to supply code signaling current of either said first frequency or said second frequency whereby the receiving apparatus at either location is rendered active to establish either said first or said second signal during a pause in the sending of a telephone current from the same location.

' ANDREW J. SORENSEN. 

